The present invention relates to a high-frequency module having a conductive cap for electromagnetically shielding a substrate and electrical components from each other, and to a manufacturing method of such a high-frequency module.
One example of conventional high-frequency modules can be found in Japanese Unexamined Patent Publication No. 8668/1999 (Tokukaihei 11-8668) (Publication date: Jan. 12, 1999). The high-frequency module (portable phone) disclosed in this publication is manufactured by a manufacturing process as shown in FIG. 18(a) through FIG. 18(e), and the product module is as shown in FIG. 18(g).
As shown in FIG. 18(a), a series substrate 917 is divided into a plurality of substrate areas. Also, as shown in FIG. 18(b), electrical components 918 make up a high-frequency circuit section. Further, a substrate 919 which is divided as shown in FIG. 18(d) is electromagnetically shielded, together with the electrical components 918, by a conductive cap 920, as shown in FIG. 18(e).
More specifically, as shown in FIG. 18(a), a solder paste is applied to a predetermined position in each area of the series substrate 917. Then, as shown in FIG. 18 (b), the electrical components 918 are placed on the solder paste thus applied. The solder paste is then melted in a reflow vessel. As a result, the electrical components 918 are electrically connected to one another via a pattern (not shown) which is formed in each area, thus forming the high-frequency circuit section in each area. Thereafter, as shown in FIG. 18(d), the series substrate 917 is divided into individual substrates 919 by dicing. Then, as shown in FIG. 18 (e), a conductive cap 920 having projections 2011 which correspond to depressions 1911 is mounted on the substrate 919. The projections 2011 are electrically connected by soldering to a metal film which is formed on the depressions 1911 and to be ground electrodes. The product as shown in FIG. 18(g) is obtained after laser trimming which is performed to adjust frequency, followed by an electrical characteristics inspection.
However, the high-frequency module of the foregoing prior art had the following problems.
That is, as shown in FIG. 19, in steps S11 through S13, the substrates 919 are provided in the form of the series substrate 917 which is yet to be divided into individual pieces, and the electrical components 918 are soldered to the substrates 919 in this state.
Meanwhile, in steps S15 through S18, the substrates 919 are provided by being divided into individual pieces. That is, S15 for mounting the cap 920 on the substrate 919, S16 for soldering the cap 920 to the substrate 919, and S17 for performing trimming are all carried out with respect to the divided individual substrate 919.
That is, the process of mounting and soldering the cap 920, and the process of trimming are repeated for each piece of the substrate 919. Accordingly, the process of mounting and soldering the cap 920, and the process of trimming need to be repeated many times. Further, automation of manufacturing steps for the divided substrates 919 requires a vast investment. It was therefore difficult to reduce the cost of the high-frequency modules.
Further, in order to meet the demand for smaller modules, the high-frequency modules are usually designed such that the electrical components 918 are provided in close proximity. Accordingly, the cap 920 and the electrical components 918 are often designed in close proximity as well.
Meanwhile, a high-temperature solder (e.g., a melting point of 220xc2x0 C. or above) has been used conventionally for the soldering in the high-frequency module. The user, on the other hand, used an eutectic solder having a melting point of 183xc2x0 C., should the user having purchased the high-frequency module carried out the reflow process by himself/herself. That is to say, despite the reflow process by the user, the solder in the high-frequency module did not melt again (though it becomes slightly soft). Thus, no movement of the electrical components 918 or the cap 920 was incurred in the reflow process.
However, to be more environment friendly and for other reasons, it has become common in recent years among users to use a Pb-free solder to carry out the reflow process. Pb-free solders generally have a high melting point, and when the Pb-free solder used has a melting point of, for example, 220xc2x0 C., it becomes essentially the same as the melting point of the high-temperature solder used in the soldering in the high-frequency module. Thus, if the user of the high-frequency module carries out the reflow using the Pb-free solder, the solder connecting the electrical components 918 and the cap 920 melts again, and movement of the electrical components 918 and the cap 920 occurs. This causes xe2x80x9csolder touchxe2x80x9d between the electrical components 918 and/or between the electrical components 918 and the cap 920. Therefore, there is demand in recent years for stabilizing the product quality of the high-frequency module by solving this problem.
The present invention was made in view of the foregoing problem, and it is an object of the present invention to provide high-frequency modules which can reduce the number of application points of an insulating adhesive and can suppress contact between components due to self-alignment which occurs in a reflow process, by applying the insulating adhesive between electrical components on a substrate.
In order to achieve this object, in a high-frequency module according to the present invention, a conductive cap provided for an electromagnetic shielding purpose is placed on a substrate on which a plurality of electrical components are mounted by soldering, and an insulating adhesive is applied between the plurality of electrical components.
With this arrangement, since the insulating adhesive is applied between the electrical components on the substrate, the insulating adhesive prevents such deficiencies as the xe2x80x9csolder touchxe2x80x9d between components due to self-alignment which is caused when the solder melts at the soldered portion in the reflow process. Thus, a highly reliable high-frequency module can be provided even when a Pb-free solder is used, and the number of application points of the insulating adhesive can be reduced.
For a fuller understanding of the nature and advantages of the invention, reference should be made to the ensuing detailed description taken in conjunction with the accompanying drawings.